Mass spectrometer apparatus



March 13, 1951 A. o. c. NIER MA SS SPECTROMETER APPARATUS 2 Sheets-Sheet 1 Filed Oct. 31, 1947 m Rm /MW QW D I E L f m I. H n

March 13, 1951 A. o. c. NIER MASS SPECTROMETER APPARATUS.

2 Sheets-Sheet 2 Filed Oct. 31, 1947 Lt-B //VV:N'TOE v 141. FEED O. C. N152 ATToENEvs Patented Mar. 13, 1951 Nr mm;

- MASS SPECTROMETER APPARATUS Alfred O. C. Nier, Minneapolis, Minn., assignor to Regents of the University of Minnesota, Minneapolis, Minn., a corporation of Minnesota Application October anion, Serial N5. 783,434..

tron source that is utilized for charging atoms or molecules so that they exist within the vessel as ions. The evacuated vessel is so constructed that it presents a path of travel for the ions, which are accelerated by a suitable potential come s; (o1. 259- 413) -1 Figure 2 is a somewhat enlarged, partially schematic side elevational view of portions of the:

gradient so that they travel along said path and collectively constitute jani electric current. The path of travel includes a certain section which is through a strong magnetic field which serves to deflect the moving ions to adegree depending upon their masses and the strength of'the mag 'netic field, whereupon after further travel they are collected and the ion current which they represent is measured or otherwise utilized.

" In instruments of this character it is essential for" proper functioning accurately to adjust the ion current path with referenceto the magnetic field; In prior instruments" of this character this adjustment has been achieved by mounting the magnet so that it may be moved, but to do so has been difiicult because of 'theheavy weight of the magnet and the degree "of accuracy required; It is an object of the present invention to pro- 'vide an improved mass spectrometer wherein the adjustment of the ion path relative to the magnetic arrangement of the instrument is conveniently effected, and to'provide an instrument in which the magnet is permanently located, and the remaining components" mounted for movement relative thereto.

- It is also an object toprovi'de an" improved y mode of constructionfor' mass spectrometers wherein themagnet is immovable'and forms the locus of mounting for the evacuated ion tube which is made so-that its position-may be adapparatus which are separated from the remaining components of thesystem in order to show the details more clearly; H

Figure 3 is a fragmentary horizontal sectional view taken in the direction of arrows 33 of Figure 1; and

Figure 4 is a fragmentary vertical sectional view taken in the direction of arrows 44 of Figure 2.

Throughout the drawingscorresponding numerals refer to the same parts. 7 p v Referring to the drawings, Figure l'partioularly, the apparatus comprises a main frame which may conveniently be composed of angle irons." The frame has afloor angle l0, posts II and I2 and intermediate frame member I3 and top frame member I4. Upon the intermediate frame member there is mounted the magnet assembly generally designated H: which may be either an electromagnet as illustrated or a permanent magnet. In any event the magnet 15 is an exceedinglyheavy part of the apparatus and is mounted directlyupon the frame members [3 in fixed position on the frame. The magnet l5 illustrated hasa core I6 and winding [3. The core; has. an air gap which is defined by pole pieces having the configuration shown by the dotted line I9. The core, which is U-shaped in plan view, has an interior opening 20 between the legs of the U and between the coil and the dusted easily and ywith reference to the magnet.

It is also an object of the invention to provide an improved mass spectrometer of simple con- 'struction, easily built at low cost and of economical maintenance.

.Other and. further objects of the invention ,are'those inherent in .the apparatus herein illustrated, described and .claimed. 1'. The invention is illustrated. the drawings in which L Figure ,1 is,a side elevationalhview of a .mass spectrometer constructed .in accordance with the invention; t I I with reference to i fastened to the frame by rear core connection Z I through which some of vthesupporting bracket structure passes, as here inaft'er defined. The entire core structure is as:- sem'bled by means of the heavy bolts 22 and is r fastening devices so as to be fixed on theframe.

' open the upper surface'ofthe core there isprovided a bracket 24 of open box formation having upwardly extending supports 25. The bracket has a cap portion 2Bwhich is provided with matching downwardly extending legs 28 which meet the upwardly extending supports 25 at the separating line 2929. The portions 25 -.25 [and 28''28 are provided with a circular "aperture 30, as shown in Figure 4, through which tom Liv MUUV. r..- it Mug. albumin-ms.

the; tubular connection 3| of the evacuat'able system is adamant pass. "The two portions 24 ndifljq tn b acket a e l fi l m tion by studs 32 which are tapped into the upper surface of themagnct core.2l. The studs are .prOi/Tided with :nuts at 33, which when pulled down i xert a clamping pressure upon the tubular con- ,nectionilt; Byloosening thenuts 33 the tubular upper surface of the core 2| at the level 35; it is possible to raise and lower the evacuatable as; sembly slight amounts for adjustment purposes.

The evacuatable assembly consistsofqaltubulart cross connection 31 which is provided at its right end, as shown in the drawings; with" a downwardly extending branch 31:whichterminatesin the flange 38. The under side of the flange 38 is ground so as to provide aspheri'cal'iseatzat. .319- which fits the spherical connection 40 oi the glass mercury difiusion pump apparatus-shown generally opposite the bracket 4!. The diffusion pump includes a vertical outlet tube 42' which leads downwardly into the moisture 'f-reezingtrap bulb 43 to which it is sealed-at 44: Fromthe trap 43 there is aside arm'45 extending to the mercury vapor pump section at 4B;- The'mercury-vapor pump is provided from the mercury boiler- 4'! which is heated by anelectrical heatingelement 48, the vaporized mercury passingupwardly through the tube i9 *and thence -to=the pumping section G6 where the-pumping action takes place and the mercury is incidentally condensed to liquid form w-hiclrretur-ns from-the --bulb 5iand thence via pipe 5itothe-mercuryboiler41'; The gases and vapors withdrawn by the mercury pump are delivered atthe-outlet tube-.52 which is connected by a-fiexible rubber hose or other flexible lead 53 to the-pipe 54, Figure 1, which leads; through thecontrolvalve 55 and line- 56,- flexible connection58-to the-fore-pump Bil which can be ofany" suitable variety--anddriven by motorfil mounted u-pon the bed plate'fi'z that is in turn mounted upon the-main frame members I0. Valve 64-provides for-breaking the vacuum when-desired and valve 55 for closing off I line -54:

The seal of thespherical connection between the glass-ball w and 'the metallic spherical-seat 39 is made-bycoating the members withordinary red sealing waxwhichisheated and the two parts pushed firmly together, after which-they arepermitted to 0001; A- cooling; coil65-is solderedto the metallic flange-38 'for;cooling the flange during gasing out operations, hereinafter described, so as, to prevent damage to the seal.

At its left end; as shownin the drawinga Fig ures 1 and'2; the tubular-cross connection 3i is joined to, the mass spectrometertube which includes an upper straight tubular section '56" of circular cross section which-is reduced-slightly at 6'! andjoined to the segmental-curved tubular section 63 which is in turn connected to; the straight tubularvsection 69 terminated in the ion collector 10. The curvedse mental.portiontflgis flattened incrosssection so as efficientlytooccupy the space between thepoleifaces l9. At the upper end of the straightsection GBFthere is a flange 12 which is arranged to be cooled by the soldered-on cooling pipe 13'. To theflange 18 there is connected/a mating fiange l4-which is held by suitable clamping bolts. Flange--14 is likewise arranged "to be cooled-''- by the -solderedon cooling coil-;-- Upon tne -flange=14 thereis mounted the entire ion source assembly shown opposite the bracket"! FWhiCh is suitablymounted and connected to the incoming leads I What arein turnconnected to the separable coupling: 91.

The ion source and its construction forms the subject matter of my application Serial No. 783,- 433, filed October 31, 1947, now Patent No. 2,490,- 278 dated December 6, 1949, wherein it is claimed. To the flange I4 there is also connected the inlet pipe 78 which extends, as illustrated in Figure 2, into the interior of the ion source delivering into the chamber 19 containingthe; elect'ronemitter filament 80. The sample undergoing analysis is introduced via tube 18 and is thus delivered into the region of the electron emitting filament 80 wheresdue' togelectron emission the sample becomes ionized. The ionized sample is withdrawn from the chamber-79 through the slit ill by a system of potential'gradient plates 82. The plates 82 serve not only to accelerate the ionized sample, butralsotofocuszitin a beam of ions which passes in the direction of the dotted line 83, thence downwardly along the tube portion 66 until it enters into the strongmagnetic field defined by the polepieces IS.- The ionized'particles of the sample benaveas an electric current" and are defiectedby the magnetic fieldalong the curved path St in anamount depending upon the strength of the magnetic field, the velocity of the particles andtheir-mass: The velocity is maintained constant or as-nearlyconstant as possible, and since thesame magnetic field is'common to allof theiomzedparticles, the amount of deflection occasioned by their passage through the strong magnetic vfield: is, therefore, dependent upon the mass of the'particles. Consequently,- the streamof ionized particles afterghaving passed throughthe magnetic field emerges asaspectrum 85,- thelighter ionized particles being" deflected most, astexemplified-"by the dotted line 86, and heavierparticles deflected least; asexemplined bythedotted line in: The ,particles are caught upon separate ion collectingp ates 88iand 890i the ion collector; mechanismn'idwhere they give uptheir.chargestothe plates; The charges upon plates 88 and 89constitutethevefiective signal and these are communicatedby leads SiLandlSl which pass out throughithewglass squash, 92 and thence through the, flexible (Sylphon bellows) housingjliito separate pre-amplifiersin the common pre-ampliner chamber, 93 which .is. cushion.- mountedby means pijthe' mounting 95 that rests upon the bracket ,liilattachediothe .framememe bers ll;

Referring to Figure 1, particularly, the .in1et tuberlllby whichlhe sample .iisiintroduced into the: mass ,spectrometerlmechanismpasses through asampling orifice 9.9, whichv is. described and claimed in my application SeriahNo- 783, 81 filed October 31,1947, and, .per se rormsnopart of the present 4 invention, the lsamplerbeing supplied at as suitable.- conta-iner. mechanism held. in. the framework 100.

Various adjuncts of the massspectrometertube include. the framework. Ill-l. which is; mounted upon the tubular cross connection 3.I,- as@shown injFigure: l. Elements-I 0 l-hasbeen eliminated in Figure Zfor purposesroficlarity The ::framework [01 which. is suitablyadjustable;- upon: tube 3| serves in turn adjustably to support-theirame joziwhich 1810f horseshoe configuration inibracsoldered on at the prescribed places.

Extending downwardly from the tubular cross connection 3| there is an interior support brace rod llll' which is clamped to the tubular connection by means of the clamping bracket I08. The brace rod Ill? extends down between the spaced legs of the large magnet l5 and is connected at its lower end to the mercury diffusion pump mechanism 4| so as to support it.

Upon the rear of the main frame there is a vertical bracket rod H9 upon which there is adjustably mounted the side arm bracket I! supporting the plate H2. The p ate H2 serves to carry an open top Dewar flask I I3 int'o'whichthe bulb 43 of the freezing trap in the mercury diffusion pump is adapted to be immersed. The brace ill may be loosened by unscrewing the wing nut us so as to permit lowering of the Dewar flask I3 for replenishing the liquid air supply therein and by the same adjustment the Dewar flask may be positioned so that the bulb 43 is submerged into the flask and yet not in contact with it.

For the most part the mass spectrometer tube is composed of an alloy such as Inconel (trademark) or other suitable high temperature alloy.

Thus, the tubular cross connection 31 and the ion path tube consisting of branches 66, e1, 68 and 69, the flanges l2 and 14 and the metallic portions of the ion collector mechanism it, as well as the branch 31' leading to the mercury diffusion pump and the branch H35 leading to the Phillips gauge are all made of such alloy. In placing the apparatus in operation itis necessary to degas it by heating these metallic parts, and yet certain areas of the apparatus must not be heated beyond prescribed temperatures, otherwise gaskets, etc. will be deteriorated. In order to provide local cooling, cooling water tubes are Thus, a cooling water tube 65 is soldered onto the flange 38, thus chilling it while the adjacent portions are heated, thus preventing the softening of the red sealing wax by which the joint 39-4i3 is sealed. Cooling water tubes are also soldered onto the flanges l2 and 74 as indicated at E3 and 15. All the cooling water tubes are connected in series or parallel, as desired. Other cooling water tubes I i 7 and I i ii extend down to t e mercury diffusion pump connections I l S and we, respectively.

It will be observed that in the described structure the entire mass spectrometertube, including the mercury diffusion pump for evacuating the spectrometer tube, and all adjuncts of the tube are mounted upon evacuatable assembly which is in turn carried on the bracket 245-25. Thus, the cross connection 3! of the evacuatable assembly has at its right end the downwardly extending branch which consists of the mercury diffusion pum which hangs as a pendulous mass at the right end, being partly supported through the connection 3? and partly through the brace rod I01. At the left end of the tube 3!, as shown in the drawings, there is the ion path defined by the tubes 66-69 having at the upper end the ion source assembly '56 and its appropriate connections and adjuncts and at the lower end the ion collector '10. In addition, all the adjuncts, including the focusing magnet assemblies 592, i533 andthe Phillips gauge I 05 are mounted upon the evacuatable assembly and are supported through it upon the brackets 24-46. Consequently, by

loosening the bracket 2423 it is possible to shift" the entire evacuatable assembly with reference to the magnet 15 and thus obtain precision adjustment of the ion beam 83 with reference to-the pole} pieces Hi. It will be noted that the pole pieces l9 define a segment of sixty degrees and that the ion source it and ion collector m are aligned as indicated at I21. The focusing and adjustment are critical, and for best results may in the present apparatus be made by a single simple adjustf' ment, whereas heretofore theadjustment has had to be made by movement of the heavy magnet [5, a cumbersome adjustment at best.

In the illustrated form of the invention the pre-amplifier 94 is mounted on the frame i I and connected to the mass spectrometer tube at, the flexible connection 93 which permits ..movement of the tube relative to the pre-amplifier case 9 4. If desired, however, the pre-amplifier may-be constructed of light weight materials and hung on the lower end of the tube 69 adjacent the ion collector plates. Likewise, if desired, the foreump 60 and its drive motor may be hung from the brace rod H11 which may also support the plate I I2 for supporting the Dewar flask [l3 of the freezing trap.

If the mass spectrometer tube is made movable and the high vacuum pump stationary so as to allow the mass spectrometer tube to be moved without moving the pump, this involves the provision of a flexible high vacuum connection between the two elements. While connections of this kind can be made by employing Sylphon bellows, they are never completely satisfactory. A Sylphon bellows has a great deal of surface area and hence is difficult to gas out satisfactorily. Moreover, they are subject to vacuum leaks. I 1 "s3 As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that I do not limit myself to the specific embodiments herein except as defined by the appended claims.

What I claim is:

1. A mass spectrometer comprising a frame, a magnet fixedly mounted on the frame, said magnet having spaced pole faces, an evacuatable system, said system having a tubular cross connection above the magnet extending in a generally horizontal direction, said cross connection having connected therewith at each end generally upright portions, the portion at one end being a vacuum pump and the portion at the other end being an ion path having unaligned straight portions connected end to end by a curved segment and an adjustable supporting means for saideva-cuatable system providing for adjustably positioning said system as a unit with reference to the frame for adjusting the curved segment of ion path with reference to the magnet pole faces.

2. The apparatus of claim 1 further characterized in that bulk of the ion path and vacuum pump portions of the evacuatable system is below the cross connection so as to form, with the cross connection, a pendulus mass.

3. The apparatus of claim 1 further characterized in that said adjustable supporting means comprises a mounting bracket attached to the magnet.

4. The apparatus of claim 1 further characterized in that the; unaligned straight portions and curved segment of the ion path, the cross 7 dn ection and the vaeuum pump. portio are all ituated inrsubst ntia ly the.- same pla e- .5. A mass spectromet rhaving a fr me a massive magnet fixedly mounted on the midportion of the frame, said magnet having fixed pole faces: and an avacuatable assembly having a generally upright mercury diffusion pump connected adjacent its upper end to one end of a transverse tubular connection of the evacuatable assembly, an ion path tube connected to the other end of the transverse tubular connection, said ion path tube comprising an ion source having an ion beam forming portions joined to a downwardly extending upper straight section connected by a curved segment to a second downwardly extending portion which is not aligned with upper straight section, said second downwardly extending portion terminating in an ion collector, the entire evacuatable assembly being a unit, means mounting said unit on the frame for adjustment movement with reference to the frame for positioning the curved section between the magnet pole faces, a fore-pump, auxiliary appliances mounted on the frame, and flexible connections between the fore-pump and the diffusion pump of the evacuatable assembly and a between .theauxiliary appliances and respective ooperating elem nts o the evacuatable assembly.

6. The apparatus of claim 5 furthercharacterized in that the auxiliary appliances includes a pre-amplifier which is mounted on the evacuatable assembly for movementtherewith.

7. The apparatus of claim 5 further characterized in that the auxiliary appliances includes a pre-amplifier, means mounting it on the frame and a flexible connection between said preamplifier and the ion collector.

8., The apparatusof claim 5 further characterized in that the evacuatable system includes a downwardly extending bulb adjacent the diffusion pump and includes a mounting on the frame for adjustably positioning a Dewar flask with said bulb extending thereinto.

ALFRED O. C. NIER.

REFERENCES CITED The following references are of record inthe file of this patent:

Nier: Review of Scientific Instruments, July 1940, vol. 11, pages 212-216. 

